In everyday life, humans are regularly exposed to and must make sense of complex acoustical sounds in their environment. While many hearing aid (HA) and cochlear implant (CI) users enjoy fairly accurate speech perception in quiet, they often experience difficulties when listening to more spectrally complex stimuli, such as music, a pervasive and culturally significant art form, and speech in background noise. These limitations are likely related to the signal processing of CIs as well as limitations in the central auditory pathways, particularly in pediatric populations with congenital hearing loss. Through investigation of complex acoustic signals at the auditory periphery, and the coding of those stimuli within the central auditory nervous system, we will deepen our understanding of why music and speech perception in noise is so challenging for hearing impaired listeners. In this study, we will investigate characteristics of the listener's auditory system, the acoustic signal input, as well as potential benefit of music training in relation to perception of spectrally complx sounds (music and speech in background noise). Our first specific aim defines the relationship between cortically generated evoked potentials, the acoustic change response, and perceptual measures of complex stimuli for a wide range of listeners, including normal hearing listeners, hearing aid users and CI recipients. In Aim 2, through within-subject comparisons, we will measure the effect that different CI signal inputs have on higher level processing of spectrally complex sounds within the auditory nervous system. Aim 3, which focus on the role of experience-dependent plasticity in perception, investigate the impact of musical training on evoked potentials and perception of music and of speech in background noise. These studies will help us to evaluate the relative benefits of specific training parameters for groups of CI recipients who vary in important factors (e.g., age, hearing profile and history), and will help us predict which individuals may benefit most from systematic training. In summary, these results could (a) expand our understanding of factors that impact perception of spectrally complex signals, (b) investigate benefits of musical training, (c) determine the extent to which training can be generalized to other tasks, like perception of speech in noise, and (d) lead to the development of more effective rehabilitation strategies.